US2509689A - Apparatus for the separation of acid and metal - Google Patents

Description

2 Sheets-Sheet 1 R. L. LUNT APPARATUS FOR THE SEPARATION OF ACID AND METAL Filed Sept. 20, 1946 May 30, 1950 F4 mmw A. Law;

3@, 1950 LUNT 2,509,689

APPARATUS FOR THE SEPARATION OF ACID AND METAL Filed Sept. 20, 1946 2 Sheets-Sheet 2:

Pate'ntec l May 30, 1950 UNITED STATES ATENT OFFICE APPARATUS FOR THE SEPARATION OF AGED AND METAL 2 Claims. 1

, This invention relates to a process and apparatus for the separation of acid and metal and is herein illustrated in some detail as applied to the recovery of pickling acid from the spent acid of a strip steel pickling plant, but certain features are adapted to be used for the production of extremely pure metal with the incidental recovery of acid with which the metal is combined.

In the pickling of metals, particularly of steel, iron and brass, large quantities of acid, usually sulphuric acid are used, and these acids gradually become contaminated or weakened, or become syrupy from contained salts, until they have to be withdrawn from use. In the past these withdrawn acids have been largely wasted, sometimes they have been simply dumped into streams, often contrary to law. Sometimes they have been neutralized with metal or even with lime and used for the production of ferrous sulfate or of venetian red, and these products have been sold below cost simply to get rid of them. The metal content of the acid wasted usually exceeds /2 1b. of metal per gallon.

In many instances in the pickling of iron, fresh acid solution is added, carrying by volume of anhydrous acid, and at the end the entire batch is ordinarily discarded and dumped, when the acid content has dropped to 10% by volume and the iron content has reached of a pound per gallon making the solution syrupy. Before this happens, ordinarily acid has been added to the solution to make up temporarily part of that used. In some plants it is customary to be adding acid all the time and to make up entirely new fresh acid solutions every 2 or 3 days, shutting down the pickling equipment, washing it out with fresh water, and running fresh water and fresh acid into the pickling tank, and heating the new acid mixture by steam to the usual pickling temperature.

According to the present invention the iron or other metal carried in the solution may be economically recovered, in the form of a very pure iron, in various states from powdered to solid forms, under favorable circumstances, so that it is useful for making special steel alloys, and for the making of pure anodes or iron.

According to the present invention, moreover, it is possible to keep the metal content of the pickling liquid low for a long period of time and to keep the acid content high. By this combination of high acid and low metal content it is possible to maintain a constant speed in pickling, avoid much of the syrupy handicap, and obtain the uniform results desired without constantly adding acid or making up fresh solution at frequent intervals.

The present invention, moreover, recovers a useful acid and a useful metal thus removing the temptation to dump the pickling residues and thus removing the temptation to pollute the streams and lakes.

Attempts have hitherto been made to recover pickling acid both electrolytically and chemically, but they failed to provide for the easy and economical removal of the metals separated out.. They involved the frequent cleaning out of clogged up cells and the breaking of short circuits formed within the cells. The cells often contained diap-hragms and many of them allowed stray currents to enter the main pickling tank. The chemical devices for recovering pickling acid also involved serious difiiculties in handling the recovered metal.

According to the present invention the foregoing and other difficulties and disadvantages are overcome and a cell is provided which needs no diaphragm, needs no added devices for prevention of stray currents, permits the cleaning of cells while the plant is in operation, reduces the consumption of labor, time and electricity, and collects the recovered metal in easily removable pails which when replaced readily seat themselves to form good electrical contacts within the cell and thus become an effectively electrically connected cathode.

In the form shown an insoluble anode rotates within the pail and is adapted to drop recovered metal on the bottom of the pail and is shown as provided with arms which rotate with it and which are adapted to knock off any electrolyte trees which may form.

The cells are preferably arranged so that the electric current goes through them in series, and the electrolyte also goes through them in series, with the result that the last cells receiving the electrolyte contain an electrolyte low in metal content and high in acid content and therefore produce loosely adherent granular deposits which may be of very pure metal and be separately collected if desired.

The series of cells are preferably so divided up that the current goes from the center of each series to the end of the series thus keeping the potential identical at each end of the device, with the result that no stray current tends to go through the pickling tank.

There are preferably at least 2 series of cells for recovery of metal and acid, so that the apparatus may run continuously, one series being shut down to enable recovered metal to be removed while current is going through the other series of cells. One advantage of this lies in the fact that it also provides smaller cathode pails for collecting the metal so that they may be easily lifted by one man. Preferably the apparatus is so operated and designed that the pails may be removed when their weight does not greatly exceed 75 lbs. per pail, thus facilitating manual cleaning.

The economy of the present invention appears when it is realized that with fifty cells in series each kilowatt hour at 100 volts delivers about 7 amperes to a cell producing about 0.01725 pound of iron and about 0.02925 pound of acid per hour per cell. Thus one kilowatt hour produces from the series of cells 0.85 pound of iron and 1.45 pounds of acid.

Thus acid is produced for about 0.74 cent a pound at the common figure of one cent per kilowatt/hour for power, if the recovered iron pays for labor and overhead.

Theoretically, therefore, it will be cheaper to recover acid than to buy acid. In fact, the efiective cost of the bought acid is much greater since the bought acid is usually discarded when onethird of the free acid in a pickle solution has been used up, whereas recovered acid is recovered in the pickling solution and none is discarded.

Moreover, the present process avoids many hazards involved in handling acid, avoids great expense in neutralizing waste acid, avoids frequent emptying and washing out of pickling tanks and avoids much of the cost of heating.

In many installations the first cost of fresh acid may be only about one-fifth of the cost of acid used plus expenses of handling and treating discard, most of which cost and expense the present invention eliminates.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Fig. 1 shows diagrammatically a pickling tank and attached recovery devices of the present invention and some other parts;

Fig. 2 is a diagrammatic cross section of a cell of the present invention.

In the form shown in some detail anode current comes through a flexible main ill and delivers the current by a slip contact brush 5 l to a Vertical shaft l2 preferably covered with rubber 63 so that the current reaches the anode is shown as screwed on to the conductor l2.

The anode M is shown in the form of a ball immersed to about the center of the glass or stoneware cell 15. A fixed cathode member H5 is shown as projecting up from the bottom of the cell E5 through a rubber or other insulating plug ll so as. to support a removable pail it having nearly vertical sides !9 which rise well above the top of the anode Hi. The cell it; is shown as provided with an entrance pipe (preferably a nonconductor rubber hose) near the cathode support It for delivering entering electrolyte horizontally into the cell l5 so that it tends to go between the three arms 2! of the cathode support it and enter the bucket ill by means of an upstanding pipe 22 in the center of the bottom of the bucket. The pipe 22 is preferably an open top rubber nozzle fitting into an opening 23 in the bottom of the bucket l8 and rising higher than any deposit of metal is likely to form within the bucket iii.

The bucket i3 is also shown with a few bottom perforations 24 between the arms 2! through which incoming electrolyte may enter the bucket l8. Preferably there are three arms 2| slanting upwardly and outwardly so that inwardly inclined bottom slopes 25, forming the bottom of the 5 bucket, rest on the cathode support arms 2| even if it is placed hastily on them and somewhat off center. The bucket is also provided with openings 26 near its top through which electrolyte tends to flow out so that it passes off through an overflow pipe 21 at the top of the cell 15 and opposite from the inlet 20.

In the form shown the outlet pipe 21 is on the line with the openings 26 and the bucket top 23 is shown as high as the top of the pipe 21 and lying close to an internal rib 29 of the cell it. The rib 29 may include an annular groove 29a so that outflowing electrolyte tends to come from the openings 26.

The rubber coating l3 of the anode shaft l2 may extend down well below the top of the bucket and carry arms 30 which will revolve with the revolving anode so as to break off any trees that tend to form on the cathode bucket with the result that they fall down and collect around the upwardly projecting pipe 22. The cathode conductor M which comes from a cathode member [6 is shown as becoming a flexible cable 32 coiled upwardly so as to be the anode main of the adjacent cell except for the last cell of the series. The cell E5 is shown as supported by a frame work 33 through intervening cushions 34.

When the cell has been operated long enough to accumulate considerable metal Within the bucket the drive for turning the anode l4, diagrammatically shown as a pulley 35, is swung upward as by pulling by a hoist ring 36 to lift the anode it out of the way and then the bucket i8 is lifted by handles diagrammatically shown as 3? inserted in some of the holes 25 and the o bucket with its solid contents is removed after allowing the solution to drain out through the holes 24 and the bucket together with its contents is placed in a suitable dump for recovered metal. The plug 22 may be removed and placed in a new bucket [8.

The bucket may be returned to the cell, or buckets may be provided of the same metal which is being deposited and the buckets may be discarded with their contents into the dump of recovered metal.

The recovered metal usually is in the form of powder or sponge falling from the surface of the cathode l9 and heaping up on the bottom of the pail l8 and is of great purity. Thus the recovered metal provides a source of highly pure iron, for example, as soon as it is washed. No short circuits can form through the trees because the trees are broken off as soon as they are long enough to be hit by the revolving arms 353 and the recovered metal is not attacked by the acid of the electrolyte because the metal and bucket are in electrical contact with the oathode support It.

Any small amount of metal which escapes through the holes 24 against the incoming current of electrolyte settles in the bottom of the cell and is readily washed out by lifting the rubber plug ll out of the bottom of the cell it being shown as tapered for the purpose so that a hose may clean out the bottom of the cell.

The anode it in the recovery of acid procedures is preferably made of lead or a lead barium alloy so as to be insoluble or of some other acid-insoluble metal. If the cell is used for the production of powdered metal, for which it is well adapted, the anode It should be of large size and of soluble metal for best results and higher current densities ordinarily should be used.

For the recovery of acid, and where recovery of the metal is of less importance, it is possible to increase the conductivity of the cell. by the addition of sulfate of alumina or alum to the solution. This cuts down the evolution of hydrogen and allows a much greater proportion of. the iron sulfate to be regenerated into acid.

The arrangement of cells and other devices shown in Fig. 2 enables recovery of pickling to be accomplished safely and economically. In the form shown in this figure, strips of metal such travel through a long tank carrythe picking acid and the pickling is maintained hot by withdrawing acid at a pipe 'll near the exit end 52 yarn which the sheets of iron are delivered and pipe ll delivers the acid to motor which forces it through a heat exchar The heat exchanger delivers the acid back into the tank @9 through a pipe i i the point where the sheets of metal enter the tank.

In the form shown the acid of the tank is so continuously circulated by withdrawing acid through a pipe near the end 92 by means of a pump and delivering it to the first cell 97 of one se ics of cells or the first cell 18 of another series of cells Hi so that the acid flows from the cell 4? through all the cells 29 of that series to the last cell 99 and thence through a pipe into the tank 39 near the entering hot acid it.

The current for operating the cells lb of each series is shown as generated in a motor generator i so as to deliver positive current to the center conductor 52 of either the cells of series 3? or the cells of the series 48. The end cells 9'9 of each series is shown as connected by a main to the negative terminal 59 of the generator and the first cells ll and 53 are likewise shown as connected to the negative terminal 59 by a main These connections provide identical potentials at opposite ends of the pickling tank and so prevent any waste of current or side current going through the tank til.

In order to enable the buckets above described to be held safely, a separate switch 58 and a separate switch 59 is provided for each end cell '39 or the series and separate switches 69 and El are provided for the end cells ll and t8 and separate switches 69, and 65 are provided between the positive conductor 96 and each half of each series of cells at the center 52. W

Generally the cells will lie in a series of 50 to 56 cells with a shunt wound generator of 125 volts.

It will be seen that there is provided a type of cell which collects cathode deposit in easily removable units, handled safely, and adapted to center themselves in good electric contact with the cathode members that no diaphragms are needed and the cell itself is easily cleaned of any deposit which interferes with its proper operation. The equipment avoids the production of stray currents, enables the cells to be used for the production of metal powders or the recovery of acid at will. In operating a pickling acid recovery plant the stronger acid is inserted where it is readily heated and works most efficiently. Moreover, the cells are so designed that any part is easily replaceable and the whole procedure is easily controlled. Since the acid is recovered continually the acid content of the pickling bath will average much higher, if desired, than in the pickling baths which have hitherto been maintained by intermittent additions of fresh acid. in the alternative the acid may be kept nearly free from salts and, being non-syrupy, will function in some ways as if strong. Moreover, the lay-product recovery metal such as iron is of extraordinary purity and ordinarily well worth recovering at a high price.

The slight loss or" acid in recovering and emptying the buckets is easily made up and is trivial compared to the loss of acid in past procedures. The number series of cells may be as great as desired so that one can always be cleaned, While the other series are being used for acid regeneration and metal recovery.

Having thus described one form of the invention in some detail, what is claimed is:

l. A circulating cell for acid separation including an acid resisting rotatably mounted anode, a conducting cathode support below the anode, a bucket cathode resting on the support and receiving its current therefrom and surrounding the anode, pipes opening into the cell for delivering acid bearing salt solution to the bottom of the cell and removing acid from its cell at the top, and an arm on the anode rotating with it and extending over substantially the height of the submerged anode and spaced from both anode and cathode and adapted to break any trees on the cathode before they reach the anode.

2. A circulating cell for acid separation includ ing an acid resisting rotatably mounted anode, a conducting cathode support below the anode, a bucket cathode resting on the support and receiving its current therefrom and surrounding the anode, pipes opening into the cell for delivering acid bearing salt solution to the bottom of the cell and removing acid from its cell at the top, and non-conducting arms on the anode r0- tating with it and extending over substantially the height of the submerged anode and spaced from both anode and cathode and adapted to break any trees on the cathode before they reach the anode.

RAYMOND L. LUNT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 223,558 Vetter Jan. 13, 1880 1,127,966 Cowper-Coles Feb. 9, 1915 1,280,213 Hach Oct. 1, 1918 1,280,249 Landry Oct. 1, 1918 1,789,443 Levin Jan. 20, 1931 1,831,934 Teufel Nov. 17, 1931 2,367,811 Urban Jan. 23, 1945

Claims (1)

1. A CIRCULATING CELL FOR ACID SEPARATION INCLUDING AN ACID RESISTING ROTATABLY MOUNTED ANOD, A CONDUCTING CATHODE SUPPORT BELOW THE ANODE, A BUCKET CATHODE RESTING ON THE SUPPORT AND RECEIVING ITS CURRENT THEREFROM AND SURROUNDING THE ANODE, PIPES OPENING INTO THE CELL FOR DELIVERING ACID BEARING SALT SOLUTION TO THE BOTTOM OF THE CELL AND REMOVING ACID FROM ITS

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